1) Field of the Disclosure
The disclosure relates generally to devices and methods for non-destructive inspection (NDI) of structures, and more particularly, to devices and methods for eddy current NDI of annular cavities, such as tapered, annular cavities, of structures of air vehicles.
2) Description of Related Art
Non-destructive inspection (NDI) of a structure typically involves inspecting the structure without having to significantly disassemble the structure and without causing harm to the structure. NDI is often used to inspect air vehicle structures, such as aircraft and rotorcraft structures, to detect any internal or external damage to the structures, for example, cracks, crack formations, corrosion, impact damage, or other types of internal or external damage, and to validate the structural health of such structures. In particular, NDI may be useful for inspecting and detecting cracks or crack formations in structures of an aircraft, such as annular cavities or bores of terminal fitting structures that attach aircraft wings to the aircraft.
Known NDI devices and methods exist for inspecting and detecting cracks or crack formations in annular cavities or bores of terminal fitting structures of an aircraft. For example, one such known NDI method of inspection and detection of cracks or crack formations of such annular cavities or bores of terminal fitting structures includes applying a fluorescent penetrant material to the interior of the annular cavity or bore of the terminal fitting structure to be inspected and observing with a black light any fluorescent penetrant material that flows into a crack or crack formation. However, such known method of using a fluorescent penetrant material typically requires that the interior of the annular cavity or bore of the terminal fitting structure be initially manually cleaned to remove any paint, grease, or other surface contaminants. Such manual cleaning of the interior of the annular cavity or bore of the terminal fitting structure to be inspected may prove challenging where the inspection area is difficult to manually access and/or observe. In addition, such known method of using a fluorescent penetrant material typically requires several applications of fluorescent penetrant to the interior of the annular cavity or bore, and several subsequent removals of excess fluorescent penetrant material from the interior of the annular cavity or bore, of the terminal fitting structure to be inspected. Such applications and subsequent removals of excess fluorescent penetrant material may be difficult to visually observe and may result in cracks or crack formations being missed by visual inspection. Moreover, such applications and subsequent removals of excess fluorescent penetrant material may be labor intensive and time consuming to perform, which may, in turn, result in increased costs for conducting such known NDI method.
In addition, a known eddy current NDI method exists for inspecting and detecting cracks or crack formations in annular cavities or bores of terminal fitting structures of an aircraft. Eddy current testing with an eddy current surface probe is based on inducing electron flow (eddy currents) in electrically conductive material. Any defect in the material, such as cracks or other discontinuities, may disrupt the flow of the eddy currents. Higher frequency signals may be used to detect surface or near-surface flaws, and lower frequencies may be used for deeper, subsurface defect detection. Such known eddy current NDI method involves manually holding a single eddy current coil against the interior of the annular cavity or bore of a terminal fitting structure and attempting to maintain a normalcy of the single eddy current coil to the annular cavity or bore, while scanning and indexing a known eddy current surface probe around the annular cavity or bore, and while watching a signal display on or connected to the known eddy current surface probe. However, such manual holding of the single eddy current coil, while scanning and indexing with the eddy current surface probe and watching the signal display, may prove challenging due to difficulty in manually accessing the interior of the annular cavity or bore of the terminal fitting structure to be inspected, and due to difficulty in maintaining the single eddy current coil normal to the interior surface of the cavity or bore of the terminal fitting structure to be inspected. These difficulties may be compounded when such known eddy current NDI method is conducted in large diameter, non-cylindrical, annular cavities or bores, such as tapered, annular cavities or bores, that are to be inspected. Moreover, it may be difficult and/or time-consuming to position and place the single eddy current coil against the tapered, annular cavity or bore of the terminal fitting structure to be inspected, due to the difficulty in manually accessing the often tight area and due to the necessity that the single eddy current coil be in proper alignment against the tapered, annular cavity or bore of the terminal fitting structure to be inspected.
Accordingly, there is a need in the art for an improved NDI apparatus and method for eddy current inspection of structures that provide advantages over known devices and methods.